Blacktop study drives smooth savings

By Karen Hunley, Samuel Ginn College of Engineering



Smooth pavements could save drivers money at the gas pump and create safe, pleasant driving conditions, even when gas prices are on the rise. A study by Auburn University's National Center for Asphalt Technology, or NCAT, and Department of Mechanical Engineering has found that smoother pavements are characterized by less rolling resistance, which requires less energy for a car when compared to a rough surface.

"It takes less force to keep your vehicle going on a smoother pavement because it's bouncing less," said Robert Jackson, faculty member in Auburn's Department of Mechanical Engineering. "A tire deforms when rolling over rough pavement, and you lose energy, and as a result, fuel efficiency."

Auburn researchers are studying and developing ways engineers and contractors can construct more fuel efficient asphalt pavements. The first phase of the study, a review of past analyses, suggests that improving pavement texture and smoothness could improve each driver's fuel efficiency by 2 to 6 percent, according to Richard Willis, assistant research professor at NCAT. He and Jackson examined several pavement characteristics and fuel efficiency studies from the U.S., Canada and Europe.

Creating long-lasting, smooth pavements that will improve a vehicle's gas mileage starts with a flexible base layer of asphalt to help prevent pavement cracking, followed by minor surface rehabilitations. These steps can help maintain smooth pavements for up to 50 years before reconstruction would be needed, saving money for budget-crunched states and drivers.

Jackson, who has a background in contact mechanics, helped with the study to clarify pavement properties that affect rolling resistance. Some research has suggested that pavement stiffness and type, whether asphalt or concrete, are major factors in controlling rolling resistance, but Jackson says it ultimately comes down to smoothness.

"If states can work to ensure smooth pavements are constructed and maintained, the general public and the state and federal governments will see the effects in their day to day budgeting," said Willis.

One roadblock to implementing smooth pavements throughout the U.S. is a lack of consistency in testing equipment and standards for concrete and asphalt roadways. Willis and Jackson agree that an experiment to better quantify more fuel efficient asphalt is still needed before agencies make any drastic changes to their pavement smoothness standards.

One method that NCAT suggests is a test trailer that can isolate tires from the vehicle, measuring the force under the tire. NCAT also uses an Automatic Road Analyzer, or ARAN, van that measures pavement smoothness. These hands-on field methods are more feasible and accurate than laboratory tests for measuring resistance on existing pavements, Jackson says.

If Jackson and Willis' continued research conclusively shows that smoother pavements lead to increased fuel efficiency, the driving public, trucking industry and government could see significant savings beyond the gas pump.

"This means that each individual has the chance to save money, and even more so for the businesses and government agencies that have much larger fleets," Willis said. "We could also see reduced costs at the grocery store because the cost to ship food would be less."

Last Updated: Feb. 8, 2012

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